Wind generator systems with associated tower structure are well known in the art. The status of such prior art is exemplified by a brief discussion of the following U.S. Patents.
Various types of wind responsive generators are known. For example, in U.S. Pat. No. 4,792,700; Dec. 20, 1988 issued to J. L. Ammons, a wind actuated rotor is disposed at the top of a single mast tower supported by guy wires. Such systems are inefficient both as to use of ground space and as to the utility of the available wind. Particularly at spots where prevailing winds exist, fields of such units may be disposed, and separate towers for each rotor limit the number of generators in such fields, increase the land costs and the tower costs per rotor. In this system, the use of a single mast tower is desirable to keep the footprint small and to keep tower costs down. However, this system is only operable at relatively modest heights of the rotor and cannot support a rotor at such heights that higher velocity winds are available, as unaffected by the shear friction with the ground at lower levels.
It has been known to cascade vertically on a single tower structure several rotors. This is advantageous in producing a smaller footprint per rotor, and in more effectively using available wind. However it introduces much greater stresses up the tower, which are difficult to deal with, particularly with a single mast type of tower. Consider that the rotors to be effective must catch and resist the wind, thereby providing great lateral forces at up-tower locations. Since wind tower generation systems must be able to withstand high velocity gusting winds, the towers therefore need to be rugged and costly. In particular consider the problems with a single mast type of tower, wherein lateral bending stresses in steel bracing tends to fatigue the metal. Thus, very costly and heavy tower structure is necessary, and in general such systems could not be made to practically operate in the presence of higher velocity winds available at greater tower heights, particularly with the added stresses of multiple cascaded rotor generator systems spaced along the height of the tower. For example W. D. Gillette in U.S. Pat. No. 4,087,990, May 9, 1978, departs from a single mast type tower to accomodate cascaded rotor structures. Similarly R. Crehore in U.S. Pat. No. 4,184,084, Jan. 15, 1980, uses a multiple masted pyramid arrangement. Nevertheless, neither system could be made practically operable at significant heights.
As taught in U.S. Pat. No. 4,217,501; Aug. 12, 1980 by W. D. Allison, increased efficiency may be achieved by aligning rotors with the wind direction. That desirable feature is offset however by the low heights and necessity to use multiple supporting towers for disposal of several rotors.
A desirable feature of U.S. Pat. No. 4,134,707; Jan. 16, 1979; M. H. Ewers is the ability to mount cascaded rotors in modular units at various tower heights. However this wind generation system is incapable of operation at any significant height above the ground, and because of a common vertical drive shaft and associated bearings has no ability to flex in the presence of high wind loads. Thus tower construction must be very rigid and expensive.
Another desirable prior art feature is outlined in U.S. Pat. No. 4,011,694; Mar. 15, 1977; F. E. Langford, namely a dynamic guy wire system for balancing the lateral forces on a tower. This system is for protection of individual guy wires to prevent overloading, and thus permits smaller guy wires to be used or protects from sudden wind gusts, etc. that exceed the capacity of the individual guy wires. However in this system a large number of guy wires is necessary to distribute the entire load, and there is no provision for the tower to flex or bend in the presence of peak loads.
A problem not adquately addressed in the prior art is that of maintenance of a wind powered generator system. Because of movable rotors, scheduled maintenance, such as for lubrication etc. is required in addition to maintenance required by catastrophic failure of any part of the system. Towers, and in particular single mast towers are not generally adapted to efficient and effective maintenance. The time of repair is critical also to the continuous generation of power, which should be interrupted as little as possible. This maintenance problem is amplified with greater tower heights. Consider for example the necessity to replace rotor structure or generator structure at heights of several hundred meters above the ground. This requires special handling equipment such as cranes, which are not conventionally available for operating at such heights, and which if provided would be extremely costly.
Accordingly it is a general object of the invention to improve the state of the wind generating art by resolving the foregoing deficiencies of the prior art and producing a more powerful and efficient generation system with small footprint adaptable to use in wind generating fields at prime locations with limited space, such as in mountain passes, and the like. Other objects, features and advantages of the invention will be found throughout the following description, claims and accompanying drawings.